(1) Field of the Invention
The present invention pertains to a drive system for a holder and heat sink for high performance, light emitting diode warning lights. In particular, the present invention pertains to a plurality of support casings for light emitting diode warning lights and their optics, where the support casings are driven by a belt and pulley drive system that converts the rotation of an input shaft to oscillating movements of the plurality of support casings.
(2) Description of the Related Art
Since the invention of the rotating beacon in the 1940's, a large number of emergency and service vehicles have been protected by warning lights that use an incandescent lamp. In these systems, the lamp is given the appearance of flashing by a rotating reflector positioned adjacent the lamp inside the warning light. The reflector is rotated about the lamp and produces a rotating, reflected light arc of coverage that provides a level of warning within a specified zone around the vehicle.
More recently, emergency and service vehicles have employed warning signal lights comprising light emitting diodes (LEDs). In most emergency warning light applications employing LEDs, it is necessary to use an optic placed in front of the LED. The optic, typically a lens and reflector, focuses the light output of the LED and concentrates and directs the light output into the particular area needed to provide visual protection to the emergency vehicle. Therefore, a typical emergency warning light assembly is comprised of a mounting structure, the LED, and the optic in proper alignment.
At the present time, some of the highest performance, commercially available light emitting diodes are built on circuit boards incorporating an aluminum base. The aluminum base permits cooling of the LED chip by conduction of the heat generated by the LED chip through the aluminum base to a metallic structure on which the base is mounted. LED assemblies of this type are commonly called “stars” because of the star shape of the aluminum base. The cooling of the LED chip is critical to the operation of the emergency warning light because the light output of the LED is substantially reduced as the temperature of the LED chip increases. In addition, the LED chip could suffer terminal failure at about 120° C.
Since the beginning of the use of light emitting diodes in emergency vehicle warning lights, their performance has continuously improved and is currently at or above 55 lumens per watt for colors such as red-orange. It has been observed that, given the forward voltage requirement of about 3 volts per LED and the voltage drop through the control electronics of a typical warning signal light, a string of LEDs in series is typically used to achieve maximum electrical efficiency on a 12 volt automotive electrical system. LEDs with a 1-watt rating typically operate at 350 milliamps. Thus, in a 12-volt automotive electrical system, the same electrical energy is required to operate one LED, two LEDs connected in series, or three LEDs connected in series. For emergency vehicle applications, it is therefore desirable to employ two or three LEDs connected in series in the warning signal lights of the vehicle. However, with the LEDs connected in series, if one of the LEDs goes out, the other LEDs go out as well. Given the substantial cost of each LED, currently between $5.00 and $10.00 apiece, it is very desirable to be able to replace, in the field, a single failed LED of a series string of LEDs in an emergency vehicle warning signal light.
To further enhance the visibility of emergency vehicle warning light assemblies, engineered systems of the high-performance warning lights have been developed. In these systems, each warning light is oscillated through an arc of movement. This moves the warning light through a zone of light projection, where the light projection is at a relatively uniform level as the light is oscillated through the middle portion of the arc of movement, and where the light projection appears to spike in intensity as the oscillating light assembly reverses its direction of movement at the opposite ends of the arc of movement.
However, in some applications the zone of light projection generated by an oscillating warning light assembly is not appropriate. In some cases it is more desirable to also have a spike in the intensity of the light projection at the mid-point of the zone of projection. This can be accomplished by employing two warning light assemblies driven by a common power source but in different synchronized arc segments. In the two synchronized arc segments of movement of the two light assemblies, each of the light assemblies is directed in substantially the same direction at one end of the arc of movement and each of the light assemblies is directed in substantially opposite directions at the opposite end of the arc of movement. An oscillating signal light apparatus that could produce these two synchronized zones of oscillating light movement through a simplified drive system construction that does not require a significant amount of space on the emergency vehicle would be very desirable.